Water-heating pool boiling of different refrigerants on the outside surface of a horizontal smooth tube

Heat transfer coefficients during pool boiling of five different refrigerants (R123, R245fa, R236fa, R134a, and R22) on the outside surface of a smooth copper tube were measured at the saturation temperature 6.7°C. Water flows inside the tube and provides heat to the refrigerants to boil. Measurements showed that the refrigerant of a higher vapor pressure has a higher heat transfer coefficient with the exception that R22 performs nearly the same as R134a. Compared with the predictions by the correlation developed from the data of electric-heating pool boiling on cylindrical tubes, the boiling heat transfer coefficients of the five refrigerants measured in this work are 30-46% higher. Among the pool boiling correlations reviewed in this work, the Cooper correlation (for pool boiling on cylindrical tubes) predicts the boiling heat transfer coefficients of R22 and R245fa reasonably well (within ±8.5%), but not as well for the other three refrigerants (R123, R236fa, and R134a). It is found that the predicted boiling heat transfer coefficients of the five refrigerants by the modified Gorenflo correlation (simply adding a constant multiplier of 1.47 to the correlation) are in excellent agreement with their respective measurements.